Inverse gas chromatography as a technique for the characterization of the performance of Mn/Zr mixed oxides as combustion catalysts

Adsorption of different volatile organic compounds (trichloroethylene, TCE; 1,2-dichloroethane, DCE; n-hexane) over different manganese-zirconia mixed oxides (MnxZr1−xO2) – widely used as combustion catalysts – was studied by inverse gas chromatography. Adsorption isotherms (calculated in the Henry region), adsorption enthalpies (ΔHads), and dispersive (γSD) and specific (Isp) components of the surface energy have been determined at infinite dilution for the investigated compounds. Both the adsorption enthalpy and the specificity of the interaction of TCE and DCE over MnxZr1−xO2 catalysts depend strongly on manganese content. Thus, the adsorption strength of the reactants over the active sites is closely related with both the surface acidity and the accessibility of the lattice oxygen. A great influence of the specific interaction on the catalytic pattern has been also noticed. Since Isp depends on the redox properties, it has been proved that the specific interaction is determined by the presence of bulk Mn3O4, which hinders the mobility of the oxygen lattice, and MnOx, with the contrary effect. Finally, the selectivity to oxidation products has been correlated with both the enthalpy of adsorption and the specific interaction parameter, decreasing the selectivity to HCl with the increase of the enthalpy of adsorption.